I seem to remember a Green Card Marriage type story for L&C, though no babies involved. It was an early S1 fic, I think.

I'm now wondering how that sort of scenario would play out maybe around the time of the John Doe for President bit, when he was swamped with bureaucratic nonsense. After all, Superman can't marry Lois Lane because she's married to Clark Kent, but he can't marry anyone ELSE either because he's already married to Lois… oy, that'd be a headache!